1. Field of the Invention
The present invention is related to compounds and methods for pyrolytically forming metal nitrides, and in particular, the present invention is related to compounds and methods for pyrolytically forming tungsten nitride and molybdenum nitride.
2. Background Art
Tungsten nitride (WNx, x=0.5-1.0) and related carbonitride phases are promising barrier materials for copper metallization in future microelectronics devices. For device applications, barrier material films must be grown in narrow (<65 nm) and deep features with perfect conformal coverage. In addition, very thin (<10 nm), defect-free films are required. Of the many possible thin film growth methods, atomic layer deposition (“ALD”) has been identified as one of the most promising manufacturing techniques for future microelectronics devices, since it can provide thin films with controlled thickness as well as perfect conformal coverage. ALD film growth entails exposure of the substrate surface to sequential pulses of two or more precursors, which are separated by inert gas purges to remove excess precursor and also to remove the reaction byproducts. To have maximum utility in ALD growth, a metal-containing precursor must be thermally stable on the surface of the substrate at the film growth temperature, but also must react rapidly and efficiently with a second reagent to provide the desired material.
While recent studies have described several different metalorganic precursors for the chemicalvapor deposition (CVD) growth of WNx films, the viability of these precursors in ALD processes is uncertain due to the requirements of excellent thermal stability and high reactivity toward ammonia in ALD growth. Most ALD processes for WNx and tungsten carbonitride films have employed WF6 and ammonia. However, use of WF6 leads to evolution of HF during the growth chemistry, which can etch substrate and reactor surfaces and can cause integration problems due to surface fluorine deposits. As a result, there is significant interest in the development of metalorganic precursors for tungsten nitride films, since they should avoid problems with hydrogen halide formation and halogen incorporation.
There have been two reported metalorganic ALD precursors to WNx. The ALD process involving W(NtBu)2(NMe2)2 and ammonia afforded WNx films between 250-350° C. The deposition was self-limiting in both ammonia and W(NtBu)2(NMe2)2, but the growth rate increased with temperature between 250-350° C. We have recently reported the ALD growth of tungsten carbonitride films between 400-450° C. using W(NtBu)2(tBu2pz)2 (tBu2pz=3,5-di-tert-butylpyrazolato) and ammonia. This process exhibited self-limiting ALD growth between 400-450° C., but also showed an increase in growth rate with increasing temperature. In CVD growth, W(CO)6 and ammonia afforded WNx films at temperatures as low as 200° C., while tungsten(VI) precursors of the formula W(NR)Cl4(CH3CN) gave WNx films with ammonia only at 450° C. or higher. Such a trend suggested to us that mid- and low-valent tungsten complexes might afford ALD growth of WNx films at lower temperatures than are possible with the two previously reported tungsten(VI) ALD precursors. W(CO)6 is unlikely to be a useful ALDprecursor, due to thermal decomposition through loss of carbonyl ligands at low temperatures.
Accordingly, there is a need for improved processes and precursors for making nitride materials.